Method of manufacturing commutators



Patented 4, 193s VUNrrlizD STATES 4 PATIENT OFFICE- Brooks Stevens, Jr., Concord,l Application September 9, 1936, Serial No. 99,905

5 claims.

This invention relates to commutators and the manufacture of the same, particularly pertaining to commutators of the type employed, for example in small electric motors. In accordance with s this invention, such a commutator may be assembled without necessity for using a hot` moulding process or employing any adhesive, while the resulting commutator may be of sturdy construction with the commutator bars firmly interlocked with an insulating core. A commutator of the type which may be manufactured in accordance with the present method is disclosed and claimed in my copending application Serial. No. 163,027, filed September 9, 1937.

16 To permitthese desirable results I preferably employ a short tube having internal ribs of dovetailed crosssection and a plurality of insulating disks having peripheral recesses to intert with the ribs of the tube. Before the tube is aembled zo with the insulating disks, its end portion may be cut away to provide small projections which may be bent over or swaged to afford a series of radial-protuberances for connection to the wiring of the armature with which the completed comg5 mutator is ultimately assembled.

Ihe insulating disks preferably may be assembled with the tube by the application of endwise pressure and at room temperature, i. e., without necessity for hot moulding. For this purpose the disks may be arranged in superposed relation in a stack which'preferably is not quite as high as the tube.v The tube may then be disposed in a suitable encircling member which prevents its expansion, and endwise pressure may be imposed by a die, preferably to force the metal of the tube into ilrm interlocking engagement with the edge surfaces of the disks. If desired, the disks may be formed of material which permits the area of each disk slightly to increase 40 when its at surfaces are subjected to high pressures, thus causing it firmly to grip the inner surface of the tube.

After the disks have been firmly engaged with the tube, the latter is cut into separate segmental 46 sections to afford the individual commutator bars.

In the accompanying drawing:

Fig. 1 is an. isometric view of a tube whichy may be employed to make a commutator in accordance with this invention;

50 Fig. 2 is a similar view of the tube after end portions havevbeen cut away to provide ka plurality of protuberances;

Fig. 3 is a similar view showing thex protuber- -ances swaged outwardly to aord radial projections;

Fig. 4 is an elevationalv view of one of the nulating disks which may be assembled with vthe Fig. 5 is a sectional view showing theLdisks and tube assembled in the die; 5

Fig. 6 is a sectional view of the commutator before the tube is cut to afford separate commutator bars; and y v Fig. 7 is an isometric view of the completed commutator.

In making'commutators of the class described, I have found it advantageous to employ short extruded copper tubes characterized by a plurality of internal ribs of dovetail cross section. In other words, the radially inward portions of 15 `these ribs are of greater cross section than their radially outward portions. Such a tube I of suitable length is shown in Fig. l, being provided with a plurality of the internal ribs 2. The end portions of the wall of such a tube may be cut away, as designated by numeral 3, between the endsof the ribs (Fig. 2). Thus portions of the wall of the tube and of the ribs project from one end of the tube, as designated by numeral 4.' The projections 4 may then be forced outwardly over the outer surface of the tube to provide avplurality of radial protuberances I integral'with the tube and substantially aligned with the corresponding ribs, as shown in Fig. 3.- y

An alternative methodof providing the pro- 30 tuberances his permitted if the tube I is originally formed from a cup-like blank. `Such a blank is commonly provided with an outer ange, and. for the purposes of the present invention, parts of such a flange may be cut away toleave 35 radially protuberant portions similar to the projections 4 of Fig. 5.

The preferred insulating core may comprise disks 5 cut from a sheet of suitable material, such as a phenol-aldehyde resin. These disks are 40 provided with a plurality of circumferential recesses 8 of dovetail shape to fit the ribs 2 of the tube I and are also provided with central circular openings 9. l

A plurality of disks-5 are assembled in super- 45 posed relation and-are then rmly secured to the tube I without necessity for employing hot moulding. For this purpose the disks preferably are disposed within the tube in a suitable die assembly, including a lower member I2 (Fig. 5) pro- 50 viding a cylindrical socket I3 in which the cylindrical portion of the tube i'its closely so lthat circumferential expansion thereof is substantially precluded. This member may also be provided with a centering pin I4* to aid the proper posi- 55 tioning of the disks 5. The die assembly also includes an upper presser member I4 which is enective in forcing the metal wall of the tube downwardly, it being noted that before the pressure is applied to the tube the height of the stack of disks may be slightly less than the height of the tube. The metal of the tube, being pressed downwardly, is unable to expand circumferentially and accordingly the cold flow of the metal results in the inner surface of the tube and the surfaces of the ribs being rmly engaged with the edge surfaces of the disks.4 Thus the cross-sectional areas of the ribs 2 and of the wall of the tube itself are slightly increased and the ribs are expanded into firm interlocking engagement with the recesses of the core material. This pressing operation is also effective in accurately defining the positions of the end faces of the protuberances 4* so that these faces are aligned with the end face of the tube. Y

It is also possible to employ disks `of insulating material which is capable of some expansion under the pressure of the die so that the flow of material takes place in the disks. Such material may be obtained which, under the pressure of the die, but without the use of a separate source of heat, increases in temperature sufficiently to permit limited flow of the particles thereof so that the area of each disk is slightly increased under the application of the endwise pressure by the die. Such material will then set rxnly in place.

It is thus evident that the core material may be secured to the tube at room temperature by the application of endwise pressure, while the tube is held against circumferential expansion, the core being secured to the tube due to the ow of the metal of the latter or due to the flow of the insulating material or due to the ow of both the metal and the insulating material. Thus the core material and the metal may be held together by a rm frictional t without necessity for employing hot moulding or any adhesive.

After the disks have been firmly joined to the tube, the wall of the tube is cut longitudinally, as designated by numeral I8, between each of the ribs 2, thus providing a plurality of commutator bars 2| which are separated from each other by air gaps, but which are firmly joined by continuous integral ribs to the core formed of insulating disks. The commutator may then be secured to the amature shaft, for example, by a press ilt.

With the form of the invention illustrated in Fig. 1, the wiring of the armature may be soldered to the protuberances 4*, while if these protuberances are not provided, the wires may be soldered directly to the end surfaces of the commutator bars.

The principles of this invention may also be employed when the core is formed of a single piece of insulatingmaterial; for example a premoulded button-like element may be joined to the metal tube inY the manner described above, as by applying endwise pressure to the tube to cause the metal ribs thereof to expand within the dovetail recesses of the core element.

Although no hot moulding operation was required in its assembly, a commutator made in accordance with this'invention is characterized by separate bars each having a continuous inthat this invention includes all modincations and equivalents which fall within the scope of the appended claims.

1. Method of making a commutator comprising forming a metal tube with a cylindrical outer surface and with an inner surface provided with a plurality of elongate ribs parallel to the axis of the tube and disposed uniformly thereabout with their radially inward parts of greater cross section than their radially outward parts, forming a plurality of disks of insulating material with similar central openings and with peripheral recesses to interflt with said ribs, assembling the disks in superposed relation with their recesses in alignment, causing the superposed disks to fit nnly within the tube with the ribs interfitting with the recesses by subjecting the tube to endwise pressure at' room temperature to cause cold ilow of the metal inwardly, while confining the tube against circumferential expansion, and then cutting the wall of the tube between the ribs to provide a plurality of separate commutawr bars each having a rib interiltting with each of the disks.

2.' Method of making a commutator comprising forming a metal tube with a cylindrical outer surface and with an inner surface provided with a disposed uniformly thereabout with their radial inwardparts of greater cross section than their radial outward parts, cutting away portions of one end of the wall of the tube between the corresponding ends of the ribs, thus leaving protuberant portions of the tube, bending said protuberant portions outwardly to aiord substantially radial protuberances, forming a plurality of disks of insulating material with similar central openings and with peripheral recesses to interflt with said ribs, assembling the disks in superposed relation with their recesses in registration, causing the superposed disks firmly to fit within the tube with their recesses interfitting with the ribs thereof by subjecting the tube to endwise pressure at room temperature to cause cold flow of the metal inwardly, and then cutting the wall of the tube between the ribs to provide a plurality of separate commutator bars each having a rib interfltting with each of the disks and having a radial protuberance for attachment to armature wiring. v

3. Method of making a commutator from atube having internal dovetail ribs and a plurality of insulating disks having peripheral recesses of corresponding cross section, comprising disposing the disks in superposed .relation with their recesses in registration and ,interiltting with the ribs of the tube, causing the superposed disks firmly to fit within the tube by pressing the tube endwise while confining it against expansion circumferentially, thus causing the metal of the tube to iiow inwardly rmly to engage the edge surfaces of the disk, and cutting the wall of the tube between the ribs to afford separate commutator bars interconnected by the insulating disks.

4. Method of making a commutator comprising forming a metal tube with a cylindrical outer surface and with an inner surface provided with a plurality of elongate ribs parallel to the axis of the tube and disposed uniformly thereabout with their radially inward portions of greater cross section than their radially outward portions, forming a core of insulating material with peripheral re-` plurality of elongate ribs parallel to said axis and wise pressure at room temperature to cause cold iiow of the metal inwardly and increase in the cross-sectional area of the ribs while coniining the tube against circumferential expansion, and then cutting the wall of the tube between the ribs to provide a plurality of separate commutator bars each having a rib intertting with the core.

5. Method of making a commutator comprising forming a metal tube with a plurality of elongate ribs parallel to the axis of the tube and disposed uniformly thereabout and having their radially inward parts of greater cross section than their with similar central openings and with peripheral recesses to interlit with said ribs, assembling the disks in superposed relation with their recesses in alignment, causing the superposed disks to fit liirmly within the tube with the ribs interiltting the recesses, by subjecting the tube to endwise pressure at room temperature 'to cause cold flow of the metal inwardly, while conning the tube against circumferential expansion, and then cutting the wall o! the tube between the ribs to provide a plurality oi' separate commutator bars each having a rib intertting with each of the disks and each having an integral radial projection at one end.

BROOKS STEVENS, Jn. 

